The present invention relates to a method and devices for wireless communication with a mobile station.
In a mobile telecommunication system the transmission quality is dependent on a wide range of radio conditions. The radio conditions vary with the distance from the base station, atmospheric conditions, the topography around the considered mobile station etc. As the radio conditions are rapidly varying for the considered mobile station, the transmission quality may sometimes deteriorate in such an extent that the connection is lost. On the other hand, when the radio conditions are good, the transmission quality may be oversized resulting in unnecessary costs. However, the problem associated with extracting a useful estimation of the radio environment of a mobile station in communication in order to predict how the radio conditions will change in the near future for a considered mobile station remains unsolved.
Having no information on the location of the mobile station in communication it is very hard to predict how the radio conditions will change in a near future for a considered mobile station. The radio network algorithms for a radio communication system are usually designed to try to follow the changes of the radio conditions and react upon the changes in order to suitably adapt electric and other characteristics when transmitting to a mobile station. However the radio environment of a mobile station is mostly changing very fast. For example, a small change in the position of a mobile station may result in a large change in received signal strength due to rapid fading. Therefore it is also mostly very difficult to accurately and rapidly enough follow the changing radio conditions. In order to improve the transmission from the base station data associated with the geographic position of the mobile station can be used. Thus, in GB-2271486 a communication system is disclosed, wherein a base station communicates with a number of mobile communication devices and is coupled to a central controller for relaying messages to the controller and for receiving and relaying control information from the controller. A number of mobile stations are provided with a GPS (Global position system) receiver in order to receive information from a GPS relating each mobile communication device to a geographic position (x, y, z). A transceiver transmits messages to the base station and receives control information from the base station. A transmitted message includes information relating to the geographic position (x, y, z) and the controller administers, through control of a base station, control of the communication system in response to geographic position information transmitted by the mobile communication devices. In the patent application GB-2271486 a method for dividing the coverage area into overlapping and non-overlapping areas and assigning different channels depending on the position of the mobile is disclosed. Signal strength decides the partitioning of the area not using any filtering of the position information. The deficiency is that said data are of insufficient quality as said data are registered for each measurement point.
WO-9801768 discloses a facility to make timing measurements between base stations and a mobile station in order to indicate the distance of the mobile station from at least one of the base stations. The distance indications in these systems will often be processed to produce an ambiguous indication of the position of the mobile station, and WO-9810768 deals with resolving position ambiguities using several techniques such as signal averaging, forming a signal contour map, making Doppler measurements, obtaining traffic flow information, and processing historical position data. In a second aspect the combination of two or more of the ambiguity resolution techniques can be achieved by multisensor fusion, probabilistic approaches, nearest neighbour and Kalman filter techniques that allow the integration of multiple sources of information over time. The preferred technique for integrating and evaluating the sequence of timing measurements is using the Kalman filter combined with probabilistic techniques to weight each of the measured events. The most likely of the sequences is chosen as indicating the true position of the mobile station. A spinoff of the technique is the ability to automatically derive signal strength contour maps. These maps can be used to improve the hand-off performance of the cellular network and for the purposes of network planning and design. The signal strength maps are continually updated, and it is hence possible to have them compensated for seasonal changes, such as tree foliage, by changing multipath and signal occlusion and this enables an automatic adaptation to any changes in the mobile network configuration. A single signal strength measurement may be susceptible to various fading influences, and a method using a single signal strength may use various signal averaging techniques to obtain a signal strength measure more indicative of the location of the mobile station. A signal strength contour map may be generated, and this map may also be used to resolve ambiguities. A system in which the method described in WO-9801768 is carried out may continuously integrate information from many sources to keep the information up to date and to compensate for the time-of-day, day to day and seasonal variations. The deficiency with the solution described in WO-9801768 is that it only deals with finding the exact location of the mobile station.
WO-9427398 discloses a method to determine the location of a mobile station using GPS, LORAN (LOcation Radio Based Navigation), triangulation or other position determining systems. Information on the geographic location, shape and size of each cell is stored in a look-up table. The position of the mobile station is constantly updated, and call management decisions, such as hand-off, can be made based on the location of the mobile station. The MTSO (Mobile Telecommunication Switching Office) has a look-up table in its data storage facilities which is used for comparing positional data from the mobile stations to data associated with the cell site coverage areas. Based on a look-up in this table, the MTSO can select the cell site, which is the most appropriate to a call. The deficiency of the disclosure of the application WO-9427398 is that the data in the database is not regularly updated.
JP-06350516 discloses a method for determining positions of mobile stations using the GPS. A receiver receives electro-magnetic waves from a measuring object of the mobile station. A statistical processor processes the amplitude of the electromagnetic waves. A controller stores the statistically processed data, based on the position information of the navigation system controller. The method according to JP-06350516 is used to determine base stations in hand-off. The data are only statically processed, and then time is not considered, which is not satisfactory in order to provide an accurate description of the radio conditions of an area around the mobile station.
The methods disclosed in the cited documents GB-2271486, GB-2313742, WO-9801768, WO-9427398, JP-06350516 deal with the position of the mobile station. None of these cited documents deals with processing incoming data related to mobile stations in a radio telecommunication system in such a way that it is possible to extract useful information concerning the radio conditions around a considered mobile station.
The deficiency is that the information is not filtered using coefficients considering area and time, and therefore the information can not be used in algorithms, which may improve the performance of the network. The termxe2x80x9cfilterxe2x80x9d is herein defined as the mathematical process by means of which the data concerning the mobile station, its position, signal quality, and other information, are processed over area and time. The termxe2x80x9cfilteringxe2x80x9d is herein defined as using the filter by means of which the incoming data are processed. The termxe2x80x9csmoothing filterxe2x80x9d is herein defined as a filter, which smoothes data concerning the radio conditions, i.e. decreasing variance of data. The termxe2x80x9cactive setxe2x80x9d is herein defined as the set of base stations, which communicate with a considered mobile station.
One object of the present invention is thus to process the information concerning the location of the mobile station by means of a filter in order to create a map of signal quality versus location. This map may be used to more accurately predict radio conditions in each zone and hence change the performance of the radio network algorithms.
A further object of the invention is to determine if a base station belongs to the active set, e.g. for soft hand-off in a CDMA system or macro diversity in general.
Another object of the invention is to force a mobile station to make hand-off earlier than scheduled due to some expected change, for example before entering a tunnel, using said processed information.
The present invention is intended to solve the problem associated with controlling the transmission in communication with a mobile station using information on the geographic position and the radio environment of the mobile station. It is made by processing the information, e.g. by means of a filter in order to smooth information, which is generally measured for specific, localised geographic positions, not for an area. This information is processed to be valid for a region according to a probability function. Then slowly varying position based information of the radio conditions is obtained which can then be used to enhance the performance of the existing radio network algorithms.
The present invention thus provides methods for processing radio condition information related to the location of the mobile station in order to improve existing radio network algorithms, e.g. algorithms for hand-off, cell selection or creating dynamic cell sizes. The initial choice of communication channel and output power could also be improved by this location dependent information.
An advantage of the invention is that it enables, using said processed information, the choice of a channel with a minimum of interference.
An other advantage of the invention is that it enables, using said processed information, the choice of power setting, in order to optimise the use of energy, i.e. to use appropriate amount of energy.
A further advantage of the invention is that it enables, using said processed information, the choice of an appropriate base station, e.g. the base station in a hierarchical cell structure providing the best quality versus power consumption.
The invention creates opportunities to enhance the performance of existing radio network algorithms by predicting the radio conditions within a specified area. It also reduces the need for highly accurate position measurements when applying the position related information in network functions since the filtering over the area smoothes the measurements made on several points in the database.
The invention also creates possibilities to decrease the size and identify the areas where certain events, such as dropped calls or failed hand-offs, often occur. This could be used to make it possible to start countermeasures against poor planning or configuration of the communication system, e.g. size and location of the cells.
The system, method and apparatus according to the invention is characterised by the features set forth in the characterising clause of the independent claims 1, 20 and 40 and their associated dependent claims.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.